Automatic transmissions or transmissions that shift individual gears operated by actuators are being increasingly used in modern vehicles, since not only is a gain in comfort achieved with them relative to manual transmissions, but so are consumption advantages. So-called double-clutch or synchronous transmissions have gained special interest, as shown, for example, in FIG. 3.
According to FIG. 2, a drive motor 10, normally an internal combustion engine, is connected via a double-clutch transmission, designated overall with 12, to a driveshaft 14, which leads to the driven wheels of a vehicle. The double-clutch transmission 12 has two partial transmissions 16 and 18 arranged parallel to each other, each with a clutch 20 and 22 and a manual transmission 24, 26. A clutch actuator 28 and 30 is provided to operate each of the clutches. The partial transmissions 24, 26 are each operated by a selector actuator 30 and 32 and a shift actuator 36 and 38. A common selector actuator and shift actuator is advantageously provided for both manual transmissions. An electronic control device 40, whose inputs are furnished relevant parameters for operation of the clutches and gear shifting, is used to control the actuators.
The design and function of such a double-clutch transmission, as well as the control device provided for it, are known per se and are therefore not explained in detail. The manual transmissions 24 and 26 cooperate, so that each of the consecutive gears is shifted by one of the transmissions, for example, the even-numbered gears by one transmission and the odd-numbered gears by the other transmission, a reverse gear being additionally assigned to one of the transmissions.
A mechanism for shifting a double-clutch transmission is described, for example, in DE 102 06 561 A1, from which FIGS. 3 and 4 are taken.
According to FIG. 3, a shift operating mechanism to operate the two partial transmissions 24 and 26 of the double-clutch transmission 12 of FIG. 3, which is modified in that only one common selector actuator and a common shift actuator is provided for both partial transmissions, contains four clutch sleeves 101, 102, 103 and 104, each of which is connected to a selector fork 105, 106, 107 and 108. One group of gears, or the gears of one of the partial transmissions 24 and 26, is operated by means of the coupling sleeves 101 or 104, the other group of gears is operated by means of the clutch sleeves 102 and 103. A first selector finger 111, which forms a shifting element, and an additional selector finger, not visible in FIG. 4, serve for engagement of gears. Gear release elements, designed as double cams 113 and 116, then ensure that, during engagement of a gear of one partial transmission, all other gears of this partial transmission are disengaged. The selector forks 105, 106, 107 and 108 are arranged axially movable on shafts 109; the selector fork clevises are designed, so that they can each be connected to a selector finger 111 or a double-cam 113, 116. For this purpose, first partial areas 114 are designed for coupling with a selector finger 111 and second partial areas 115 are designed for coupling with double cam 113. For engagement of a gear, the selector finger 111 enters into connection with the end region 110 of the corresponding selector fork 105 or 106, the selector shaft 112 being moved in the axial direction. At the same time, the double cam 113 is connected to the corresponding selector fork 107 or 108, which belongs to the same group of gears or to the same partial transmission. Rotation of the selector shaft 112 pivots the selector finger 111, so that the selector fork 105 or 106 on shaft 109, and therefore also the corresponding clutch sleeve 101 or 102, is displaced and the corresponding gear is engaged. At the same time, rotation of the double cam 113 causes disengagement of the previously engaged gear of the same transmission, if this was assigned to a different shift track.
If a double-clutch transmission is not involved, but an ordinary transmission with only one clutch and one drive train, double cams acting as gear release elements are connected to all additional selector fork clevises, so that it is guaranteed that during engagement of a new gear, a previously engaged gear is disengaged. In a double-clutch transmission, the mechanism permits engagement of the new gear with simultaneous disengagement of the previous gear of the corresponding partial transmission, or disengagement occurring just beforehand, the gear engaged in the other partial transmission remaining uninfluenced by a gear shift in the partial transmission just shifted.
The selector shaft 112 generally has a shoulder (not shown in FIG. 4), with which its axial movability is limited to a narrow angle range, in which the selector finger 111 in the depicted example is roughly perpendicular, and the ends of the double-cams 113, 116 are flush with the corresponding cutouts in the end regions 110 of the selector forks. Rotatability of the selector shaft 112 from the rotation position with a perpendicular selector finger 111 for engagement of a gear by movement of one of the selector forks along the shaft 109 in one or the other direction is only possible at a predetermined axial position of the selector shaft 112. This limited adjustability of the selector shaft 112 can be caused by the fact that the shoulder rigidly connected to the selector shaft 112 engages in a template, in which, for example, the pattern according to FIG. 4 is left open in a five-speed transmission with reverse gear.
In the depiction according to FIG. 4, W is designated as selector track. S1 to S3 denote shift tracks, in which the gears R, I, III, III and IV, V lie. The selector shaft 112 (FIG. 3) is movable by means of a selector actuator, for example, the selector actuator 32 of FIG. 2, in the direction of selector track W, and rotatable by means of a shift actuator, for example, the shift actuator 36, around its longitudinal axis, if the selector finger is situated in one of the shift tracks S1, S2 or S3.
The position of the selector finger and the additional elements rigidly connected to the selector shaft 112 is recognized in the control device 40 in known fashion, for example, by the fact that an incremental counter is assigned to each of the actuators 32 and 36, which records a change in position of the selector shaft in the selector or shift direction. By referencing the counter states at specific stops, for example, an end stop on the end of the selector track W and an end stop on the end of one of the shift tracks, the absolute position of the selector shaft 112, with respect to the selector and shift operation, is known.
In order to check the functional reliability of the transmission, it is expedient, as shown by engagement of second gear with reference to FIG. 4, to travel to an end stop SII of the shift track S2 during or immediately after engagement of a gear, and to verify achievement of this end stop in the control device 40. On reaching the end stop SII, one of the side edges R1, R2 of the shift track S2 is advantageously approached further, in order to verify the corresponding position of the selector shaft. After reaching stop SII and one of the edges R1 or R2, perfect function of the shift mechanism is guaranteed, and it is also guaranteed that the second gear is engaged.
A peculiarity of the procedure just outlined is that the shifting element, or the selector finger in the depicted example of FIG. 4, is situated in the position designed PII when second gear is engaged and remains in this position as long as a new gear is not required. If a new gear, for example, fifth gear, is required, the shifting element must be moved from position PII from the shift track S2, into the selector track W, then along selector track W to shift track S3, and then in shift track S3 into position PV. This long path is naturally connected with a relatively long duration, which elapses from the requirement for engagement of fifth gear to actual engagement of fifth gear.